1. Technical Field
The invention relates to an apparatus and a process for the shaping of a glass piece, especially in a closed-forming system, into a hollow glass article and namely, to a rough or final product, especially by means of producing machines working by the series principle, such as IS and RIS and other glass-working machines by means of a presettable plunger which can be driven into the glass piece. The plunger is movable from a loading position to a final pressing position, is speed regulated, and is also preferably pressure regulated.
2. Background Art
Machines for the production of hollow glass articles, such as the so-called IS and RIS machines working as series machines are known. In these known machines, the production process takes place at several production stations arranged one after the other. At each production station, the same production step takes place on one or on a plurality of pieces of glass. Therefore, the work cycles on the different pieces of glass are displaced in time. For the production of a hollow glass article, liquid drops of glass are pressed, or blown into a meal pre-mold to form a rough product, the so-called blank. After transferring this blank to the finish mold assigned to the pre-mold, the blank is formed in the finish mold into the finished product by blowing out or evacuating.
The drop of glass falls from above into the glass pre-mold closed at the side to the lower opening of which is connected a mouth tool. The drop falls on a plunger which is positioned in a loading position and which is variable in its height position. A bottom of the mold then closes the upper part of the mold. By means of a piston in a piston-cylinder arrangement, the plunger can be moved vertically up and down. After the closing of the pre-mold with the bottom of the pre-mold, the plunger through an upward movement presses the glass against the forming contour of the pre-mold and also against the contour of the mouth tool and the bottom of the pre-mold to give the glass the desired inner and outer contour at the same time. The liquid glass is limited therefore, for a short period of time at its total inner and outer surface by contours defined by the mold, and completely fills the free volume of the mold. When the liquid glass drop falls into the pre-mold, the plunger is in its loading position at which is closes the mouth opening of the mold in part. Only for the molding of the liquid glass is the level struck into the glass, and as a rule produces at the same time the mouth of the hollow glass article.
In this known glass-forming apparatus and process, the level, known in the art in the past and still today as a "plunger", is moved forward and backward pneumatically. Here, the loading position, as the lower outlet position for the present hollow glass article, can only be sufficiently positioned and changed with very great loss of time by means of distancing bushings or so-called "loading screws". Another disadvantage is the need of regulating the pneumatic pressure for each individual plunger. This pneumatic pressure must be so dimensioned that the mouth of the blank is completely formed. The pneumatic pressure may lie between about 0.4 and 1.5 bar, and must be empirically determined from quality control of the finished hollow glass article for each individual plunger. Changes in property value of the liquid glass might also lead to changes in quality. This necessitates another change of the pneumatic pressure.
However, with the known process and apparatus, the cycle of forming cannot be changed independently of other influencing factors. Instead, the pressure for advancing the plunger, the forming speed, and the static pressure on the glass and the mold system depend directly on the time axis and can only be changed slightly in part or not at all.
From EPO 165 012 A1 are known a process and an apparatus of the kind mentioned. Here the plunger is moved hydraulically according to a set time frame, whereby at given times, the speed course for the plunger can be preset. For the purpose, the computer is continually fed with external time pulses. A Hall sensor with a piston rod designed in screw form on its outer surface is used as a position sensor, and a pressure sensor is used to indicate the fluid pressure existing against the plunger. Through a computer arranged after these two sensors, the amounts of pressure and the supply of the hydraulic fluid moving the plunger can be varied according to the ratio between actual and desired values. This process has the disadvantage in that only a time frame for the individual flow phases is taken into consideration, whereas the continued position pattern of the plunger will not be taken into consideration so that the speed errors lead to unpredictable final positions of the plunger. It has been recognized that in this way, a sag in uniformity of product quality can result. It was further learned that in this known process, the plunger provided only speed measurements. The pressure was taken into consideration in this process, however, regulation of the pressure level in relation to time set in when the highest pressure position of the plunger is reached, that is, when the pressure between the plunger and the piece of glass stops movement of the plunger. It has been found especially harmful to the quality of the glass when the pressure against the plunger, as proposed there, is increased still more after reaching the stopped position of the plunger. The pressure regulation dependent on time is also a disadvantage, however, if it has been carried out during the forming step. Namely, it has been found that only when taking into account of the particular position of the plunger does a pressure change lead to the desired quality improvement or improvement of the uniformity of the quality of the glass article, while a pressure variation dependent on time very easily leads even to a worsening of quality or at least to a higher rate of rejects.